Abstract: An analytical method for obtaining Eigenvalues of structures with hinges is proposed. The method uses a new external force called the folding force which is a pair of equal and opposite moment loads, and derives the fundamental equation in such a way that hinges are built into a temporary continuous system in which the hinges are neglected. This method will be applied conveniently to some structures, provided that the static response, natural frequencies, natural modes, and the bending moments for the deformation of the modes of the temporary continuous system are obtained easily. Two examples are shown to verify the proposed approach.